RFR: 8294594: Fix cast-function-type warnings in signal handling code [v3]

[Aleksey Shipilev]

> After [JDK-8294314](https://bugs.openjdk.org/browse/JDK-8294314), we would have signals_posix.cpp excluded with cast-function-type warning:

Aleksey Shipilev has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains five commits:

 - Merge branch 'master' into JDK-8294594-warning-cast-function-type-signals
 - Naming
 - Redo using the proper signatures
 - Merge branch 'master' into JDK-8294594-warning-cast-function-type-signals
 - Fix

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Changes: https://git.openjdk.org/jdk/pull/10494/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10494&range=02
  Stats: 10 lines in 4 files changed: 0 ins; 2 del; 8 mod
  Patch: https://git.openjdk.org/jdk/pull/10494.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10494/head:pull/10494

PR: https://git.openjdk.org/jdk/pull/10494